Solar Panels On Roofs Facing Different Directions? Then You Need To Do This.

As you can see, it has solar panels on 2 separate roof areas. In solar jargon, you would say there are 2 “strings” of solar panels.

The main string is facing North, which is the best roof orientation for solar panels. These panels should get the optimum amount of sun throughout the day.

The smaller string is facing East. These panels will get 15-20% less sunlight than the panels facing North.

Obviously the installer could not fit all the panels on the North facing roof. Fair enough.

If your home will require solar panels on multiple roof areas, which face different directions, then you should use a special type of inverter to ensure that you still get good system performance.

Multiple Roof Areas Require Multi String Inverters

If you have solar panels facing different directions then you need a Multi String Inverter (also called a Multi MPPT inverter) with one string/MPPT for each roof area.

In order to maximise output from your solar panels, each roof area’s panels must be connected to a separate inverter string that has its own Maximum Power Point Tracker (MPPT). The MPPT is a bit of electronics that optimises the power from the panels. It is impossible for an single MPPT to work optimally if it is connected to panels which are facing different directions.

[ For the technically minded people the reason for this is that the IV Curves are different for each roof area because they get a different amount of irradiance from each string of panels. This means there are 2 maximum power points to choose from and an MPPT can only optimise properly to 1 maximum. ]

If you are using a reputable solar company then they will employ a CEC accredited solar designer to individually design each homes solar system, and take stuff like this into account. If you ask to see the design drawing of your solar system they should show you it. For the solar system above, it would look something like the sketch below – notice how it clearly shows each string is wired into its own MPPT in the inverter.

If your system is not designed like this then the string of solar panels with the least sun shining on it at any one time will drag the other panels’ power down to its low power output. This will reduce your power output. If your solar installer cannot provide a diagram like this as part of your quotation (and more importantly as part of your final contract when you are ready to buy) then move quickly on to a more professional firm.

UPDATE: June 2013

Thanks to Martin in the comments below for pointing out that, since I wrote this post, an alternative option has come to the market in Australia: micro inverters. Micro inverters are a fantastic new technology whereby each panel is has its own inverter, and there is no central inverter at all. This means that every panel is optimised independently and you can have as many roof areas pointing in as many directions as you want. You can read lots more about the pros and cons of microinverters here. I’m a fan – I have 6kW of the little beauties on my roof in sunny Radelaide.

UPDATE: March 2016

Thanks to Hagen for pointing out that using the phrase “This will cripple your power output” is an exaggeration, so I changed it to “This will reduce your power output” . In the example in the line diagram, due to the configuration of the strings the power output will be reduced slightly, with a single MPPT, not crippled. In other configurations the power reduction could be much more. A good solar installer will quantify all this for you as part of the design documentation.

Hi Flinn
Looking at purchasing a 3kw SMA sunny boy inverter and using 250watt bosch panels x 12.
What are your thoughts? Am i making the right decision.
The company is Aus 1 solar. Has anyone used this company??

HI Finn,
I’ve got a 2kw system on max. rebate due to run out in Jan. 2020.
I have 18 panels totalling about 3.6kws supporting it on a single string East/West configuration.I reckon I can accommodate another 20 panels, – and if they were all say 250’s, thats about 9.5 kw – 8 of those new panels would be North facing, with 2 East, 2 west and 8 south, so I would guess we could capture up to about 6kw an hour on a good day.
Should I upgrade now or wait till the big subsidy expires?

3.6 kilowatts is a large system to have on a high feed-in tariff. Economically I’m certain you’d be far better off waiting for your high feed-in tariff to expire. If you are motivated by environmental concerns you could get a large system installed now would reduce emissions, but you could do the same by helping a relative or charity get solar.

I have a similar setup in mind ,10 North , 2 east, 2 West then 10 South . Question, How many strings would this setup require and would it be better to use microinverters? 3 Phase
Current setup is 8 facing North single inverter 2 KW single Phase on three Phase home supply.

The 10 north and 10 south facing panels could be attached to one string inverter with the north facing panels on one inverter MPPT (Multiple Power Point Tracker) and the south facing panels on the other inverter MPPT. Technically, I suppose it would be possible to put the remain 2 east and 2 west facing panels on a small single MPPT inverter. But rather than pay for those 4 panels and a second inverter you would probably be better off skipping them and using the money you save to buy higher capacity north and potentially south facing panels. If you decide you want to have the east and west facing panels then putting them on microinverters isn’t a bad option as they will perform slightly better and the cost for just 4 panels can compare well to the cost of a 4 panel string inverter installation.

Hi Flinn
Looking at purchasing a 3kw SMA sunny boy inverter and using 250watt bosch panels x 12.
What are your thoughts? Am i making the right decision.
The company is Aus 1 solar. Has anyone used this company??
Flinn the panels are c-si M60 Eu 30117
The inverter is sunnyboy 3000TL

Hi all, I have just been offered a 4.5KW system using LG panels and a sunny 5000 inverter for $8207 from aus1solar.. the old saying of it sounds too good to be true is ringing in my ears, but the price is too good to completely ignore!

My work collegue is having some difficulties getting AUS1SOLAR to complete the work (5Kw Bosch system) at her house. Apparently everything is installed (29 Dec 2012) but not yet working (9 Jan 2013).
Luckily she has not fully paid them yet. They keep ringing her asking for the remaining money but she refuses to pay until they complete the work.
Good prices and good equipment yes but do not pay until fully installed and working.
You have been warned.

Hi Finn
We are in process of designing and building our own house. We have plenty of north facing roof but there is one section which the roof has angle of about 10degree and its away from the rest of roof bulk.
We would like to allow for at least 10-12 panels on it.
Do we still need 2 inverters or can all areas use same inverter as they are all facing north. Is the distance of inverter to panels a factor that needs to be considered?
Thanks in advance.

Hi Finn
I am really glad I found your website. Having started looking at where we and how we can site solar panels, I am able to weigh into the duscussions with the solar company and ensure that I am happy with the final result. Your site is soooo informative and very interesting. I am now happy to proceed with installations knowing I have had a base check on what is being proposed. Thanks Again

We will be installing east and north facing panels on a 2 story home. The north facing panels are all on the upper story with no overshadowing concerns. The east facing panels are on 2 roof spaces ( upper and lower floors) and will consequently shade at different times.
Looking to put TIGO optimisers on both of the east facing sets of panels. The northern panels would not be optimised.
Would this work ok? Do we need multiple arrays for the inverter?

If you are not going to put Tigos on all the panels facing both North and East, then you really need to use an inverter with 2 MPPTs. There are lots of inverter options and they cost no more than single MPPT inverters, so this should not be a problem.

If you only have Tigos on the East facing panels then, in the morning the north facing panels will get less sun than the east facing panels and drag the whole array down. It would also violate the Australian Standard AS5033 from my understanding of it.

Interesting. Does this apply to a yacht where the 2 panels are almost horizontal but one is angled 5% left and the other 5% right? What sort of 12v regulator is required when you have several banks of panels pointing different directions? Thanks.

I have 16 solar panels in a 3.04 Kw solar array, with a 5 Kw inverter. The most the readout has ever read is 2.6Kw. I have room to add 2 more panels. can they just be attached and is it simple to do. What do I need to watch out for. is it economic to source secondhand panels.

The generalization in the article makes it incorrect. With identical strings, single-MPPT inverters can handle strings with different orientations. The Fronius research findings to that effect were referenced on Whirlpool.

I can only have panels installed on roofs facing east or west. I intend to have a 5kw one. With this roof orientation, is it worth the expense? Should it be all panels on the East side or the West side? Or is it best to have it split on both roofs?
Thank you.
Denise

Hi Fynn,
With off grid home would North west be the better to still keep worst month power to charge batteries. Or still best to stay North as the worst in June has the sun over the horizon before as we get home to cook tea anyway. The summers and long days we have ample power anyway.

I have a roof facing northeast that fits 5 modules and another roof facing northwest that fits 6 modules. Currently in Brazil, there is no certified micro inverters and that prevents me to use them.

I am researching for a dual mppt inverter, to connect two string 1 with 5 modules in series and another with 6 modules series. The point here is that I am afraid that will not have the necessary DC voltage for the input on most of the inverters.

Do you have any suggestion in this case? If I connect all the 11 modules in series and connect to the inverter, my generation will be highly impacted?

G’day Marcos,
Five panels connected in series will produce on average ca 150V. The minimal input voltage for an inverter is usually around 80V. So, a dual-MPPT inverter will be able to handle your panel strings.
Cheers,
Josip

I’ve just ordered a system using 14x 290W panels and a Fronius Primo 3.5kW inverter. The installers have just been here but sadly had to cancel due to wet weather, however they were able to do some measurements to determine panel placement and found that they can only fit 13 panels on my main north-facing roof. Splitting the strings between multiple north aspects will mean they end up with cabling that’s too long. They’ve recommended a North/West split.

I’m wondering if you could provide some guidance on my options and what would be better.

I live in the Bundaberg area. My north facing roof is not quite north (approx. 10 degrees), the west facing roof is approx 280 degrees. They’ve suggested 8x panels on the north face and 6x on the west face.

I work from home – running a small aircon most days along with a few computer monitors, laptop etc. I want to run as much as I can off the power I’m generating during the day so will schedule dishwashers, washing, charging of devices etc etc. There are only two of us living in the house.

Would I receive more benefit from dropping one panel and having 13x north facing, or stick with the 14x panels split as detailed above? How would the peak power generation look with the split configuration – am I likely to see a longer peak? Is the inverter still sized appropriately for this sort of configuration?

The closest location it has information for is Gladstone, but conditions are similar enough to make a reasonable comparison.

According to PVwatts 13 panels, which comes to 3.77 kilowatts, at 10 degrees orientation will produce 6,308 kilowatt-hours over a year.

Eight panels, or 2.32 kilowatts, facing north at 10 degrees will produce 3,882 kilowatt hours while 6 panels, or 1.74 kilowatts, facing west at 280 degrees will produce 2,569 kilowatt-hours. This comes to a total of 6,451 kilowatt-hours.

So according to PVwatts you can expect to produce around 2% more electricity with 8 panels facing north and 6 facing west than with 13 north. In addition, their production will be slightly lower at noon and slightly higher later in the afternoon which will improve self consumption and help provide power for afternoon air conditioning.

While conditions in Gladstone will be a little different from Bundaberg, it seems very likely you’ll be better off with one extra panel and having them face two directions.

The 3.5 kilowatt inverter can have up to 4.66 kilowatts of panels put on it and as 14 panels is only 4.06 kilowatts you are fine. You could even add two more panels and still be within the limit. (You may want to ask the installer if that’s possible.) The inverter can handle two strings or sets of panels, with each string facing a different direction, so that’s not a problem.

Great thread. I’m new to solar and further to above want some general guidance on the benefit of splitting an array on both the north and west facade.

I have a new house, and space for panels on the north side of my roof but also could squeeze some on to the western side. Common sense tells me that if I use micro inverters or multiphase inverter then splitting the system would allow me generate more energy over a longer period. I live in western sydney and get western sun until about 7-8pm in summer. I hardly ever see panels split like this. Is there a reason?

Ps. I’m waiting on quotes And will run this by the installers but wanted a bit of prelim advice.

It is definitely possible to have two arrays of solar panels on your roof, one facing north and one facing west. In Sydney west facing panels will produce an average of about 15% fewer kilowatt-hours than north facing panels. You can use microinverters but all except the smallest string inverters (the most common type of solar inverter) have two MPPTs (Multilple Power Point Trackers) that allow two independent arrays to be attached. Note with string inverters it is possible for there to be limits on how different the two arrays are in size.

Using optimizers or panels with panel string optimization can also allow panels to be placed facing different directions.

You must have an extremely small roof if you can’t fit a 2 kilowatt system on. Or maybe the problem is your roof is both small and difficult to install on. Usually, if a roof is difficult to install on the problems can be worked around by using panels with microinverters, DC optimizers, or by using panels that have panel string optimization, as these allow panels to be placed facing in a variety of different directions.

But assuming there is no room on your roof for panels, it is possible to place them on racks on the ground. But this will require unshaded ground space and you may require permission from your council.

If you are looking for other ways to save energy you can look into insulation, LED lighting, energy efficient appliances, and so on.

I have been offered 24 x 270 watt panels with a 6.5kw with Aussie Solar, I live in the south of the Gold Coast QLD, But i was told from another company who also quoted me said in my area we are only allowed 5.5kw due to single phase power . We have a domestic home.

On the main grid in Queensland households with single phase power can install up to 6.66 kilowatts of solar panels. Unless you are in a very rural area for the Gold Coast you should be on the main grid.

Love the information in this article but one question I have that’s not covered with a single or multiple string is does the number of panels matter. Ie do strings need to have equal or even planels, such as 2, 4, 6 or 8 or can they be any combination as long as the total output is under the inverters capacity?

When an inverter has two MPPTs the two separate arrays of panels can have different capacities. But inverters can have restrictions on how different the arrays can be and even restrictions on how how different their orientation can be, so that is something to watch out for. Total panel capacity can be one third more than the inverter capacity.

ABB inverters for residential use have up to 2 MPPTs (Multiple Power Point Trackers) which means they can have panels facing in up to 2 different directions. But this limitation can be overcome if solar panel optimizers are used or if the panels have cell string optimization.

I realise this question is specific to my own needs but if you can give me answer I will appreciate it.

I have high voltage panels that mean they run at about 59. My 600KW inverter has failed and I am being told that the only way to be safe for a replacement is to split my 10 panels into two strings and install a multi string inverter. The technical guy told me he would take two panels off the roof and run a cable through to do the job. It occurs to me that this could be problem in as much as how does one easily make the first cable stop at teh 5th panel and likewise the second cable do the same when my 10 panles are firmly fixed to the roof?

I don’t know how your panels are currently arranged, but in order to make the single string you have now into two separate strings, whoever is working on them will need to unplug the connectors between the two middle panels so there will be 5 panels on one side and 5 on the other. Lengths of cable will be attached to those detached connectors and run down to the new inverter. This will make two separate loops of cable or strings, each with 5 panels. Two panels will be temporarily removed for access. There’s no real chance of getting the wrong number of panels on a string unless the person doing the job can’t count to five.

My solar contractor has proposed a north and west facing system for me, 10 panels north and 7 west, Trina Honey M 305w panels on a 5kW Fronius. We use quite a bit of power in the afternoon to early evening so the intention is to have reasonable capacity on the West especially in summer. The contractor recommended that a minimum of 7 panels needed to be on the west string to ensure the inverter ran to capacity. I would have preferred an 11/6 or 12/5 split to maximise northern generation.
We are only using 3 dc optimisers on the system for some potential minor shading issues.

So my question is whether what he’s saying regarding the inverter capacity is correct?

Inverters can require a minimum number of panels be connected to each inverter MPPT (Multiple Power Point Tracker). Your inverter will have two of these. The number of panels needed depends on the type of inverter. You can check this at the Fronius configurator which is here:

I don’t know what your exact inverter model is but after a quick look it does appear the configurator will allow you to put more than 10 panels on the north facing section of roof. But there could be other reasons why the installer recommends a 7/10 split such as shade issues or it simply may be difficult to fit more than 10 panels on the north facing roof.

I have a new system on a new house with 9 North facing panels and 21 West facing panels. I am seeking some efficiency gains so have asked the installer (local electrician) about wiring and panel facing. Apparently (info from speaking with electrician as they have not been able to provide me with a diagram) they have wired up the system as 15 + 15, not 9 + 21. The inverter is Fronius 8.2-3 Symo.

My understanding is that due to Australian standard (ASNZ 5033 clause 2.1.6) the panel facings should all be on one string (i.e. West and North separate). Alternatively we could parallel the 9 north panels with 9 of the west panels into 1 MPPT. The other MPPT could have the 12 other west panels in a single string.

If your system has north and west facing modules on the same string that would violate installation guidelines unless they have optimizers. Section 7.1.3 of the Clean Energy Council Install And Supervise Guidelines For Accredited Installers states:

“7.1.3 Modules that are electrically in the same string shall all be installed at the same tilt angle (±5 degrees) and orientation (±5 degrees), unless using DC conditioning units or micro-inverters.”

So unless those panels have optimizers (DC conditioning units) your installer should either install optimisers or rewire it. (Australian consumer law protects you in this case regardless of what warranties the installer may or may not have provided.) The only possible out is if Fronius says that configuration is okay, but this is very unlikely.

The installer has finally agreed that it is currently wired poorly. Perhaps my citing of the guidelines spurred them into action (thanks for the name & section #). It does worry me that this installer may have tried the same thing on other less-aware consumers in the past. They initially tried to pass some blame onto us for requesting that some panels be moved (from their initial 30 west-facing setup to our requested “maximum north-facing” which turned out to be 9 north/21 west).

The agreement that I expect to make this week is to have one panel moved from north to west so that 1×8 string for MPPT1 and 2×11 string for MPPT2 (somewhat akin to the dfiagram in the article above except it won’t be 1×3 and 2×3). This seems to be the best compromise as I don’t think that we can mount any more than 9 panels on the north without some complicated racking.

Thanks for your advice. Let’s hope that we can now get a little bit more efficiency from our system.

I have 5.5kw system just installed 2 days ago, inhave 2 face 10 panel is North face 0 tile, 8 panels west face 30 tile, I realised one thing that they installed my system as single mppt. I added my circuit picture. Could you please tell me if this is correct or not.

You should be fine because that’s just a simplified diagram and not a detailed wiring diagram. If you had them send you the proper wiring diagram should definitely show the two solar panel arrays attached to separate MPPTs.

Many thanks for your great work.
I’ve recently had a few quotes for a 6.6kw system. And one supplier mention that he was only able to fit max 13 x 330Wh panels per string with a Fronius 5.0 inverter. Is this correct?

DC voltages have to be prevented from exceeding a maximum of 600 volts and I would expect the maximum voltage of a 330 watt panel in a string to be around 45-46 volts. This means 13 of these panels would commonly be the maximum as that would add up to around 590 volts. There can be mild differences between different makes of panels, but 13 is probably the maximum.

Yes I agree we only can have 13 panel max on a string on a series configuration due to the limit in voltage per string.

What if we have a “polystring” configuration which consists of two series of 13 panels, and the two series are wired in parallel and then will be connected to a MPPT on the inverter. Then we still maintain the max Voltage (which is 590 volts as you pointed out, even we will have double the current generated by a series of 13 panels). Then we can in theory can fit 13×2=26 panels on a MPPT?

I am no electrician nor engineer, and those are what I’ve learned from the net. Please let me know what you think of the above design.

It is certainly possible to have two strings of panels in parallel and connected to one MPPT to meet the Australian 600 volt DC limit. The two stings will need to have the same number of panels in them. But what can be done will depend on what the inverter’s MPPT can handle.

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